A sash window arrangement disposed within a frame is well known. The frame is comprised of a pair of opposed vertical tracks or jam. The tracks are adapted to slidably guide a pair of sash windows within the frame.
Various types of balance systems are known and are used to counterbalance the weight of the sash window. In particular, block and tackle counter balance assemblies are known and have become popular due to their combination of relatively compact size and ease of installation. The block and tackle balance combines a system of pulleys and an extension spring mounted within a rigid balance channel for conversion of a high spring tension applied over a short working distance to a lower tension applied over a longer working distance. The extension spring is anchored at one end of the balance channel and the pulley system is anchored at the other end of the channel.
A traditional arrangement utilizing a block and tackle balance is disclosed in U.S. Pat. No. 5,530,991 to deNormand. In deNormand '991, an end of the balance channel is is attached to the track via a hook or other intermediate structure. An end of a cord woven through the pulley system and extending from a second end of the channel is attached, via a hook or other intermediate structure, to a shoe. This shoe is in turn attached to the window sash and slides therewith, within the track. An inverted block and tackle counterbalance system is disclosed by U.S. Pat. No. 6,041,476 to deNormand. In this arrangement, the end of the cord extending from the channel is attached to the track via a hook or other intermediate structure. The balance channel is then attached to the sash shoe via a hook or other intermediate structure such that the balance channel slides within the track as the window slides within the frame.
If the sash is pivotable, typically the shoe includes a braking mechanism which expands within the channel, to prevent the sash from moving upwards when tilted. While such braking mechanisms are effective, they are relatively complex and expensive, and rely on friction for braking. This results in a need for tight part tolerances.
The present invention is provided to solve these and other problems.